I did have a spare dog, however someone other than my wife ran him over.....
As for a spare wife - remember, she's the one on the lawnmower and the chances of her running over herself are slim to none.
As for generators - I only have one, however, I do have 3 sump pumps, a spare to kick in when a part breaks on pump 1, a battery backup one to kick in when the power goes out.